fix(mindspace): ensure thumbnail sidecars for WeChat link card og:image

Generate SVG/PNG sidecars at HTML delivery and after share-preview repair so
forwarded service-account links get a raster og:image when only meta exists.

Co-authored-by: Cursor <cursoragent@cursor.com>

wechat/verify/share-preview-repair.mjs

@@ -3,6 +3,7 @@ import path from 'node:path';
 import { injectBeforeDocumentClosingHead } from '../../html-document-injection.mjs';
 import { normalizeCoverMetaSuggestion, upsertMindspaceCoverMeta } from '../../mindspace-cover-meta.mjs';
 import { preparePublishedPlatformBrand } from '../../mindspace-page-tag.mjs';
+import { scheduleWorkspaceHtmlThumbnailSidecars } from '../../mindspace-workspace-thumbnails.mjs';
 import {
   artifactFileExists,
   resolveArtifactLocalPath,
@@ -126,6 +127,12 @@ export function repairArtifactSharePreview(artifact, { topic = '', publishDir =
   if (!verified.ok) {
     return { ok: false, reason: verified.reason ?? 'repair_incomplete', changes };
   }
+  if (publishDir && artifact?.relativePath) {
+    scheduleWorkspaceHtmlThumbnailSidecars(
+      publishDir,
+      String(artifact.relativePath).replace(/\\/g, '/'),
+    );
+  }
   return { ok: true, reason: null, changes };
 }